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Ppmbrighten User Manual(0)					       Ppmbrighten User Manual(0)

NAME
       ppmbrighten - change a PPM image's Saturation and Value

SYNOPSIS
       ppmbrighten [-normalize] [-saturation [+|-saturation_percent]] [-value [+|-value_percent]]
       ppmfile

       Minimum unique abbreviation of option is acceptable.  You may use double  hyphens  instead
       of  single  hyphen to denote options.  You may use white space in place of the equals sign
       to separate an option name from its value.

DESCRIPTION
       This program is part of Netpbm(1)

       ppmbrighten increases or decreases the Saturation and Value (from the HSV color space)  of
       each  pixel  of a PPM image.  You specify the per centage change for each of those parame-
       ters.

       You can also remap the colors of the pixels so their Values cover the full range of possi-
       ble Values.

       Hue-Saturation-Value,  or  HSV,	is one way to represent a color, like the more well-known
       RGB.  Hue, Saturation, and Value are numbers in the range from 0 to 1.  We always capital-
       ize  them  in  this  document when we mean the number from the HSV color space, especially
       since "value" as a conventional English word has a much more abstract meaning.

       Value is a measure of how bright the color is, relative to some specified maximum (the PPM
       format  is  also defined in terms of a specified maximum brightness -- For the purposes of
       this program, they are the same).  In particular, it is the brightness  of  the	brightest
       primary color component of the color divided by the maximum brightness possible for a com-
       ponent.	Zero Value means black.  White has full Value.

       Hue is an indication of the secondary color with the same  brightness  that  most  closely
       approximates  the color.  A secondary color is made of a combination of at most two of the
       primary colors.

       Saturation is a measure of how close the color is to the color indicated by  the  Hue  and
       Value.	A  lower  number means more light of the third primary color must be added to get
       the exact color.  Full Saturation means the color is a secondary color.	 Zero  Saturation
       means  the  color is gray (or black or white).  Decreasing the saturation of a color tends
       to make it washed out.

       If it is impossible to increase the Value of a pixel by the amount you specify  (e.g.  the
       Value is .5 and you specify +200%), ppmbrighten increases it to full Value instead.

       If  it is impossible to increase the Saturation of a pixel by the amount you specify (e.g.
       it is already half saturated and you specify +200%), ppmbrighten increases it to full Sat-
       uration instead.

       For  a simpler kind of brightening, you can use pamfunc -multiplier simply to increase the
       brightness of each pixel by a specified per centage, clipping each RGB component where the
       calculated  brightness  would  exceed  full brightness.	Thus, the brightest colors in the
       image would change chromaticity in addition to not getting the specified brightness boost.
       For decreasing brightness, pamfunc should do the same thing as ppmbrighten.

       ppmflash does another kind of brightening.  It changes the color of each pixel to bring it
       a specified per centage closer to white.  This increases the value and saturation.

EXAMPLES
       To double the Value of each pixel:
       ppmbrighten -v 100

       To double the Saturation and halve the Value of each pixel:
       ppmbrighten -s 100 -v -50

OPTIONS
       -value value_percent
	      This option specifies the amount, as a per centage, by which you want to change the
	      Value of each pixel.  It may be negative.

       -saturation value_percent
	      This option specifies the amount, as a per centage, by which you want to change the
	      Saturation of each pixel.  It may be negative.

       -normalize
	      This option causes ppmbrighten to linearly remap the Values of the pixels to  cover
	      the  range 0 to 1.  The option name is wrong -- this operation is not normalization
	      (it was named in error and the name has been kept for backward compatibility).

	      ppmbrighten applies the brightening that you specify with the -value  option  after
	      the remapping.

	      Before  Netpbm  10.14  (March 2003), your input must be from a seekable file (not a
	      pipe) to use -normalize.	If it isn't, the program fails with a  bogus  error  mes-
	      sage.

SEE ALSO
       pnmnorm(1) , ppmdim(1) , pamfunc(1) , ppmflash(1) , pamdepth(1) , pnmgamma(1) , ppmhist(1)
       , ppm(1)

AUTHOR
       Copyright (C) 1990 by Brian Moffet.  Copyright (C) 1989 by Jef Poskanzer.

       Permission to use, copy, modify, and distribute this software and  its  documentation  for
       any  purpose  and  without fee is hereby granted, provided that the above copyright notice
       appear in all copies and that both that copyright notice and this permission notice appear
       in supporting documentation.  This software is provided 'as is' without express or implied
       warranty.

netpbm documentation			 26 October 2012	       Ppmbrighten User Manual(0)
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